Surface structure of CTMA modified bentonite and their sorptive characteristics towards organic compounds

This work was to examine the correlation between surface structure and sorptive characteristics of cetyltrimethylammonium cations (CTMA⁺) modified bentonite, which will provide novel information for exploring the sorptive mechanisms of organoclays. Various amounts of CTMA⁺ (0.21–1.98 mmol/g) were intercalated into bentonite to prepare a series of organobentonites with different structures. N₂ adsorption–desorption isotherms were plotted for the organobentonites to obtain the surface structure information, and sorption capacities of these organobentonites toward phenol, aniline, nitrobenzene and naphthalene were examined. It was shown that surface areas, pore volumes and surface fractal dimension of the organobentonites decreased with increasing CTMA⁺ loading amount. Sorption capacities of the organobentonites towards the four organic compounds have no evident correlation with their surface structures, and K_oc values of the organic compounds were shown to first increase until the maximum and then decrease as CTMA⁺ loading amount further increased. Combining with the surface structure and sorption capacities of the organobentonites, we proposed that the solute molecules were penetrated into the CTMA⁺ aggregates, and partition rather than adsorption mechanism dominated the sorption processes. The CTMA⁺ aggregates formed optimal partition phases in the intermediate surfactant loading range.